package QualificationRound.Sum;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main
{
	private static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

    public static void main(String[] args) throws IOException
    {
    	String str = "";
        while((str=br.readLine()) != null)
        {
        	if(str.equals(""))
        		continue;
        	int num=Integer.parseInt(str);
        	System.out.println((1+num)*num/2 + "\n");
        }
    }
}